This invention relates to a magnetic recording medium having an organic coating as a sliding surface, particularly to a magnetic recording medium having excellent durability.
Magnetic recording media have been widely used in a variety of fields as media for a large capacity information recording and reproducing apparatus. There are magnetic tapes as recording media for voices, communications, etc.; floppy disks as digital signal recording apparatus; hard disk media as peripheral recording apparatus for large-scale computers; etc. These recording media are expected to increase in their recording capacities and at the same time required to have reliability bearable for long time operation.
In the case of magnetic recording media, information is usually written and read out while conducting sliding with a head. In a special case, there is employed an apparatus wherein a medium and a head do not slide and information is written and read out while maintaining a very narrow, constant distance between the medium and the head. In this case, it is admitted that the head and the medium are subjected to a contact sliding with a certain probability.
An increase of recording capacity inevitably makes the sliding conditions severe and thus the improvement in durability is an essential requirement. There has been obtained no medium having sufficient durability.
In order to improve the durability, it is proposed to use a lubricant for reducing friction and wear at the time of sliding. For example, a long-chain fatty acid derivative such as oleic acid or stearic acid as a lubricant is impregnated into a magnetic recording medium layer. This method is mainly used for a so-called coating medium wherein a mixture of magnetic particles and a binder is coated on a support member. But, since the lubricant gradually flies off from the surface, it is difficult to expect lubricating properties for a long period of time.
In order to improve such a disadvantage, it is proposed a process for coating a fluorine series lubricant which is more excellent in lubricating properties on a disk surface. According to this process, a sufficient effect can be obtained at an initial stage, but the lubricant is peeled off when, used for a long period of time, resulting in undesirably reducing the effect.
On the other hand, in order to prevent the peeling of the lubricant at an initial stage, it is proposed to fix a fluorine series lubricant on the surface of the medium (U.S. Pat. No. 4,120,995). The fluorine series lubricating compound is represented by the formula: EQU R.sub.f --O--(CH.sub.2).sub.n SiX
wherein R.sub.f is a perfluoroalkyl group; n is an integer from 2 to 10; and X is halogen, cyanide or alkoxy group, and is a lubricant which reacts with a metal film surface or oxide film surface, followed by fixation. According to the process for fixing the fluorine series lubricant represented by the formula mentioned above on the magnetic layer surface, since the reaction system is on the solid surface, the reaction is difficult, and it is difficult to obtain a uniform reaction film and very difficult to apply such a process to a practical production line. Further, since the molecular weight of the fluorine chain is too small to exhibit a lubricating effect, the durability of the magnetic layer is not improved sufficiently.